A number of methods for applying a cladding layer to aluminum strips or sheets, respectively, are known from the prior art.
In roll-cladding, sheets are made from a cladding material and placed on a core ingot. The sheets and the core ingot are then hot-rolled to form a composite material. However, only holohedral cladding layers having in each case a single thickness and alloy composition per layer may be produced using this method. Cladding of only a partial area or a cladding layer which selectively has different thicknesses across the ingot width or length, or is composed of a plurality of alloys of various compositions has not been possible to date, since this would lead to extremely asymmetrical balances of forces in the rolling gap, such that a very irregular or warped product, respectively, would be produced, or the roll stand could even be damaged.
In cast cladding, a cladding layer is directly cast onto a core ingot while the latter is being cast. The core ingot in its original form is thus directly formed as a composite material. Even with this method, only holohedral cladding layers having a single thickness and of a single alloy may be produced, since the rolled ingot, i.e. the core ingot having the layer applied, otherwise would not have a planar but rather a stepped rolled face.
A further possibility for applying cladding layers lies in the use of brazing pastes which are mechanically or manually applied using cannulas during the processing of the aluminum strips and sheets. This method has the disadvantage that the carrier substance of the brazing paste has to be removed without residue prior to brazing the workpiece, for example by way of evaporation, which on account of insufficient ventilation is problematic in particular in the case of closed structures. Furthermore, only very narrow regions can be coated using the brazing pastes, and the thickness of the solder layer can also only be controlled in a comparatively crude manner by way of the amount of paste or the composition of the latter, respectively.
A further alternative lies in the use of a brazing foil which, however, is rather expensive. Furthermore, the brazing foil typically has to be manually applied onto the workpiece in a complex fashion. Moreover, the brazing foil is also suitable only for comparatively large material thicknesses, since the brazing foil otherwise would be very thin and extremely difficult to process. Any application of the brazing foil to very small regions is hardly manageable in technical terms.
There besides, further methods which are less widely used, for example explosive cladding, cold-roll cladding, or similar methods are known in the prior art. However, all of these methods are complex and expensive. Furthermore, only holohedral cladding layers having a single thickness and alloy composition on the surface may be produced using these methods in conjunction with hot-rolled strips.
Furthermore, DE 600 06 567 T2 discloses the production of an integral aluminum alloy structure in which an inlay is inlayed into a fluted bed of a core and is then connected thereto by hot rolling. On account thereof, scabs on the edges of the structure are to be avoided.
Using most of the afore-described methods, in particular hot-roll cladding which is widely used, only holohedral cladding layers across the entire strip may be produced. Other methods are very complex or not economical.
A holohedral cladding layer is not required or is even often disadvantageous in many applications.
For example, a solder coating is only required in specific regions of a component made from a strip or a metal sheet. However, when the strip and thus also the component produced therefrom as a consequence of the process is completely coated with solder, more solder may accumulate at the brazing point than is required for brazing, such that erosions or other undesirable effects may arise. Moreover, in the case of a holohedral solder coating, unintentionally brazed connections of two components which are disposed so as to be close to one another may arise.
Furthermore, many cladding layers are more ignoble than the core alloy and thus more prone to corrosion. On account thereof, increased material removal due to corrosion may arise. Furthermore, cladding layers such as solder coatings typically have a visually less appealing surface than non-clad surface regions. Furthermore, solder coatings of AlSi alloys often have large Si depositions which have a disadvantageous effect during deformation of the strips, since they may induce cracks and reduce elongation at break.